The present invention relates generally to improvements in electronic photoflash devices and it relates more particularly to an improved electric shockproof electronic flash device for use in photography.
In general, the conventional electronic photoflash device whether separate from or incorporated in a camera body employs a high voltage direct current, so as to produce an electric gas discharge in a flash tube. This high voltage for use in such an electronic flash device includes a DC to DC voltage step-up convertor or network for raising the voltage of a DC electric current supplied from a low voltage power source such as a battery and storing the stepped-up voltage in a storage capacitor. With such an arrangement, the high voltage direct current is stored in the internal circuit or storage capacitor while the flash device is switched on. Such an electric network is generally disposed internally of the flash device in a manner to be electrically insulated from the exterior thereof, for the operator's protection so that the likelihood of the high voltage reaching the exterior is minimized.
However, should water enter or penetrate such a flash device, a current would flow from the high voltage portion of the insulating substrate on which the electric circuit is printed, to an external portion of the device due to the electrical conductivity of the penetrant water thus imparting a high voltage to these external portions which are also rendered conductive, with a resulting high risk that a large current may be discharged into the body of an operator, if the operator touches the high potential external portion of the flash device. Such occurrence or accident may occur even with a water-proof flash device or a water-proof camera having a self-contained flash device, although such a flash device or camera is designed as to be protected against the penetration of any water. However, while used in water or in rain, such a water-proof flash device or water-proof camera is likely to be moistened with water which diffuses into or otherwise penetrates the device or camera leading to the aforesaid type of accident. Accordingly a structure which eliminates the possibility of the high voltage of an electronic photoflash network from reaching the accessible exterior is highly desirable.
An electronic flash device equipped with an electric shock preventive mechanism has heretofore been commercially available. This commercially available type electronic flash device includes a pair of mutually spaced metallic plates disposed in a suitable or desired portion in the photoflash device, such as at the rear of the photoflash reflector and a discharge network for causing the discharge of electric energy from the main photoflash capacitor is also included in the photoflash network with actuating terminals therefor connected to respective metallic plates. With such a device, in the event that water penetrates into the photoflash device, then two metallic plates are short-circuited by the water to actuate the discharge network, thus causing the discharge of electric energy stored in the main capacitor and the operator is thus protected from electric shock.
However, with the aforesaid structure in which water entering the device is detected by a pair of spaced metallic plates, the photoflash device possesses the drawback in that in the event of water entering the photoflash device through portions having no sensing metal plate, the discharge circuit remains unactuated. Furthermore, such a device requires the pair of metal plates for detecting the presence of water as well as a special circuit for effecting the discharge of electric energy from the main storage capacitor, resulting in a complex construction and a costly device.